Low emission, non-oxygenated fuel composition

ABSTRACT

Provided is an unleaded gasoline fuel which is substantially free of oxygenates, and most preferably contains substantially zero oxygenates. The gasoline fuel also has a Reid vapor pressure less then 7.5 psi, a sulfur content less than 30 ppmw, an aromatic hydrocarbon content between 25 and 30 volume percent, and/or a 50% D-86 Distillation Temperature between 210 and 220° F., and/or a 90% D-86 Distillation Temperature between 300 and 330° F., and the fuel composition fails the California Predictive Model requirements for emissions. Preferably, the olefin content of the fuel is also 8 volume percent or less. Such a gasoline fuel offers a substantially oxygenate free gasoline which avoids the environmental impact of oxygenates, yet when combusted in an internal combustion automobile provides good performance and good emissions, despite failing the California Predictive Model. The gasoline fuel in particular can provide surprisingly lower NO x  emissions than that predicted by the California Predictive Model.

The present application is a continuation application of U.S. Ser. No.09/071,793, filed May 4, 1998, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fuels, particularly gasoline fuelswhich are substantially free of oxygenates. More specifically, thepresent invention relates to a low-emission gasoline fuel which, uponcombustion, provides surprisingly low emissions, particularly ofnitrogen oxide emissions, and is also substantially free ofoxygen-containing compounds.

2. Brief Description of the Prior Art

One of the major environmental problems confronting the United Statesand other countries is atmospheric pollution caused by the emission ofpollutants in the exhaust gases and gasoline vapor emissions fromgasoline fueled automobiles. This problem is especially acute in majormetropolitan areas where atmospheric conditions and the great number ofautomobiles result in aggravated conditions. While vehicle emissionshave been reduced substantially, air quality still needs improvement.The result has been that regulations have been passed to further reducesuch emissions by controlling the composition of gasoline fuels. Thesespecially formulated, low emission gasolines are often referred to asreformulated gasolines. In California, low emissions gasoline is oftenreferred to as California Phase 2 gasoline. One of the requirements ofthese gasoline regulations is that, in certain geographic areas,oxygen-containing hydrocarbons, or oxygenates, be blended into the fuel.

Congress and regulatory authorities, such as CARB (the California AirResources Board), have focused on setting specifications for lowemissions, reformulated gasoline. The specifications, however, requirethe presence of oxygenates in gasoline sold in areas that are not incompliance with federal ambient air quality standards for ozone, and thedegree of non-attainment is classified as severe, or extreme. Among theemissions which the reformulated gasoline is designed to reduce, arenitrogen oxides (NO_(x)), hydrocarbons (HC), and toxics (benzene,1,3-butadiene, formaldehyde and acetaldehyde). A reduction in theseemissions has been targeted due to their obvious impact upon the air webreathe and the environment in general.

There is increasing attention from environmental agencies to the needfor a reduction in emissions of nitrogen oxides. NO_(x) emissions areknown precursors for smog created in metropolitan areas. Most of theNO_(x) emissions are man-made, with gasoline fueled engines generatingabout 24% of the man-made NO_(x) emissions. NO is the major constituentof NO_(x) emissions from combustion processes. NO is a precursor of NO₂in the atmosphere and a critical constituent in the formation of ozone.NO₂ can irritate the lungs and reduce respiratory function. NO_(x) canbe an important precursor to secondary formation of particulates,according to the “National Air Quality and Emission Trends Report,”1992, Office of Air Quality Planning and Standards, U.S. EnvironmentalProtection Agency, EPA 454/R-93-031, October 1993. A reduction ofnitrogen oxides, particularly in large metropolitan areas such as LosAngeles and Sacramento, Calif., and many eastern U.S. states, would bemost valuable. As a consequence of all these harmful effects, thereformulated gasolines have been designed to reduce NO_(x) emissions.

Oxygenated gasoline is a mixture of conventional hydrocarbon-basedgasoline and one or more oxygenates. Oxygenates are combustible liquidswhich are made up of carbon, hydrogen and oxygen. All the currentoxygenates used in reformulated gasolines belong to one of two classesof organic molecules: alcohols and ethers. The Environmental ProtectionAgency regulates which oxygenates can be added to gasoline and in whatamounts.

The primary oxygen-containing compound employed in gasoline fuels todayis methyl tertiary butyl ether (MTBE). While oxygen is in most casesrequired in reformulated gasolines to help effect low emissions, thepresence of oxygenates in gasoline fuels has begun to raise legitimateenvironmental concerns. For example, the oxygenate methyl tertiary butylether has been observed in drinking water reservoirs, and in a fewinstances, ground water in certain areas of California. As a result, thepublic is beginning to question the benefits and/or importance of havingcleaner burning gasolines, if they simply pollute the environment inother ways. Furthermore, oxygenates also have a lower thermal energycontent than non-oxygenated hydrocarbons, and therefore reduce the fueleconomy of gasoline fueled motor vehicles.

Thus, while some of the concerns with regard to gasoline fuelscontaining oxygenates, such as methyl tertiary butyl ether, could beovercome by further safe handling procedures and the operation ofpresent facilities to reduce the risk of any spills and leaks, thereremains a growing public concern with regard to the use of oxygenates ingasoline fuels. In an effort to balance the need for lower emissiongasolines and concerns about the use of oxygenates it, therefore, wouldbe of great benefit to the industry if a cleaner burning gasolinewithout oxygenates could be made. A cleaner burning gasoline resultingin low NO_(x) emissions would be of particular benefit to theenvironment in light of the increased attention to reducing nitrogenoxide emissions. The availability of such a gasoline, which containedsubstantially no oxygenates, would allow the public to realize theenvironmental benefits of low emissions, yet ease the concern ofpotential contamination of ground waters, and the environment ingeneral, with oxygenates. Of benefit to the industry would also be sucha low emission gasoline which contained substantially no oxygenates andalso offered more flexibility to refiners in blending the gasoline.

Accordingly, it is an object of the present invention to provide agasoline fuel which can truly benefit the environment and offer goodperformance.

It is another object of the present invention to provide a gasoline fuelwhich provides good emissions, yet is substantially free of oxygenates.

Yet another object of the present invention is to provide alow-emission, substantially oxygenate-free gasoline fuel which exhibitssurprisingly low NO_(x) emissions when combusted in an automobileinternal combustion engine.

Still another object of the present invention is to provide a gasolinefuel which provides good emissions and also permits more flexibility torefiners in blending the gasoline.

These and other objects of the present invention will become apparentupon a review of the following specification and the claims appendedthereto.

SUMMARY OF THE INVENTION

In accordance with the foregoing objectives, the present inventionprovides an unleaded gasoline fuel which is substantially free ofoxygenates, i.e., the fuel contains less than 1.0 weight percent oxygenbased on the total weight of the fuel composition, and most preferablycontains no oxygen containing compounds. The gasoline fuel of thepresent invention also has a Reid vapor pressure less than 7.5 psi, asulfur content less than 30 ppmw, more preferably less than 20 ppmw, anolefin content of no greater than 8 volume percent and an aromatichydrocarbon content between 25 and 30 volume percent, and/or a 50% D-86Distillation Temperature between 210 and 220° F., and/or a 90% D-86Distillation Temperature between 300 and 330° C. The fuel compositionalso does not meet the emissions performance criteria of the CaliforniaPredictive Model for emissions. Such a gasoline fuel offers asubstantially oxygenate free gasoline which avoids the environmentalimpact of oxygenates, yet when combusted in an internal combustionautomobile provides good performance and good emissions, despite failingthe present California Predictive Model requirements.

In particular, surprisingly low NO_(x) emissions can be observed for thegasoline fuels of the present invention, with the NO_(x) emissions beingsubstantially lower than that predicted by the California PredictiveModel established by the California Air Resources Board (CARB). GoodPerformance with surprisingly low NO_(x) emissions can be obtaineddespite the fact that the gasoline fuel of the present invention doesnot meet the specifications for the CARB reformulated gasoline fuel, andfails the California Predictive Model. The gasoline composition of thepresent invention is substantially free of oxygenates, does not meet theflat limits for at least one, if not more, of the aromatics, T90 and/orT50 requirements set for the new (Phase 2) reformulated gasoline, andfails The California Predictive Model for emissions. Nevertheless, thegasoline fuel of the present invention allows one to enjoy goodemissions, and particularly surprisingly low NO_(x) emissions, whilealso avoiding the potential problems of oxygenates. For it has beensurprisingly found that when one controls the amount of sulfur inaccordance with the present invention to less than 30 ppmw (and morepreferably less then 20 ppmw), and in particular when one controls theamount of sulfur together with olefins in accordance with the presentinvention to less than 8 volume percent, it is possible to haveadditional flexibility with respect to the other regulated fuelproperties, i.e., aromatics, T90 and T50, in a non-oxygenated fuelwithout sacrificing low emissions.

In another embodiment of the present invention, there is provided amethod for operating an automotive vehicle having a spark-ignitedinternal combustion engine. The method comprises introducing into theengine an unleaded gasoline which is substantially free of oxygenates inaccordance with the present invention. The unleaded gasoline is thencombusted in the engine. In a preferred embodiment, the automotivevehicle also has a catalytic converter through which at least some ofthe engine exhaust emissions created by combusting the unleaded gasolineare introduced, with the resulting emissions then being discharged fromthe catalytic converter and subsequently to the atmosphere. Goodperformance and surprisingly low NO_(x) emissions are realized uponusing the unleaded gasoline of the present invention in the operation ofan automobile.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to gasoline compositions havingproperties which minimize the amount of exhaust pollutants, particularlynitrogen oxides, emitted during combustion, while also overcoming thepotential detrimental impact, environmental and otherwise, ofoxygenates. In particular, the gasoline formulations of the presentinvention provide emissions of nitrogen oxide which are surprisingly lowin that they are much lower than predicted by the California PredictiveModel developed by CARB. While the compositions of the present inventionoffer such surprising low emissions, as well as good performance as agasoline, they also offer the advantage of avoiding the problemsinherent with oxygenates, as the gasoline formulations of the presentinvention are substantially free of oxygenates.

Gasolines are well known fuels, generally composed of a mixture ofnumerous hydrocarbons having different boiling points at atmosphericpressure. Thus, a gasoline fuel boils or distils over a range oftemperatures, unlike a pure compound. In general, a gasoline fuel willdistil over the range of from about, room temperature to 437° F. (225°C.). This temperature range is approximate, of course, and the exactrange will depend on the conditions that exist in the location where theautomobile is driven. The distillation profile of the gasoline can alsobe altered by changing the mixture in order to focus on certain aspectsof gasoline performance, depending on the time of year and geographiclocation in which the gasoline will be used.

Gasolines are therefore, typically composed of a hydrocarbon mixturecontaining aromatics, olefins, and paraffins, with reformulated gasolinemost often containing an oxygen compound, i.e., an oxygenate such asmethyl tertiary butyl ether. Gasolines may also contain variousadditives, such as deposit control additives, demulsifiers, corrosioninhibitors, and antioxidants. The fuels contemplated in the presentinvention are unleaded gasolines (herein defined as containing aconcentration of lead no greater than 0.05 gram of lead per gallon whichis 0.013 gram of lead per liter). The preferred fuels will also have aResearch Octane Number(RON) of at least 90. The anti-knock value (R+M)/2for regular gasoline is generally at least 87, and for premium at least92.

In an attempt to reduce harmful emissions upon the combustion ofgasoline fuels, regulatory boards as well as Congress have developedcertain specifications for reformulated gasolines. One such regulatoryboard is that of the State of California, i.e., the California AirResources Board (CARB). In 1991, specifications were developed by CARBfor California gasolines which, based upon testing, should provide goodperformance and low emissions. The specifications and properties of thereformulated gasoline, which is referred to as the Phase 2 reformulatedgasoline or California Phase 2 gasoline, are shown in Table 1 below.

TABLE 1 Properties and Specifications for Phase 2 Reformulated GasolineFlat Averaging Fuel Property Units Limit Limit Cap Limit Reid vaporpressure psi, max. 7.00¹ 7.00 (RVP) Sulfur (SUL) ppmw 40 30 80 Benzene(BENZ) vol. %, max. 1.00 0.80 1.20 Aromatic HC (AROM) vol. %, max. 25.022.0 30.0 Olefin (OLEF) vol. %, max. 6.0 4.0 10.0 Oxygen (OXY) wt. % 1.8(min) 1.8 (min) 2.2 (max) 2.7 (max)² Temperature at 50% deg. F. 210 200220 distilled (T50) Temperature at 90% deg. F. 300 290 330 distilled(T90) ¹Applicable during the summer months identified in 13 CCR,sections 2262.1(a) and (b). ²Applicable during the winter monthsidentified in 13 CCR, sections 2262.5(a).

In Table 1, as well as for the rest of the specification, the followingdefinitions apply:

Aromatic hydrocarbon content (Aromatic HC, AROM) means the amount ofaromatic hydrocarbons in the fuel expressed to the nearest tenth of apercent by volume in accordance with 13 CCR (California Code ofRegulations), section 2263.

Benzene content (BENZ) means the amount of benzene contained in the fuelexpressed to the nearest hundredth of a percent by volume in accordancewith 13 CCR, section 2263.

Olefin content (OLEF) means the amount of olefins in the fuel expressedto the nearest tenth of a percent by volume in accordance with 13 CCR,section 2263.

Oxygen content (OXY) means the amount of actual oxygen contained in thefuel expressed to the nearest tenth of a percent by weight in accordancewith 13 CCR, section 2263.

Potency-weighted toxics (PWT) means the mass exhaust emissions ofbenzene, 1,3-butadiene, formaldehyde, and acetaldehyde, each multipliedby their relative potencies with respect to 1,3-butadiene, which has avalue of 1.

Predictive model means a set of equations that relate emissionsperformance based on the properties of a particular gasoline formulationto the emissions performance of an appropriate baseline fuel.

Reid vapor pressure (RVP) means the vapor pressure of the fuel expressedto the nearest hundredth of a pound per square inch in accordance with13 CCR, section 2263.

Sulfur content (SUL) means the amount by weight of sulfur contained inthe fuel expressed to the nearest part per million in accordance with 13CCR, section 2263.

50% distillation temperature (T50) means the temperature at which 50% ofthe fuel evaporates expressed to the nearest degree Fahrenheit inaccordance with 13 CCR, section 2263.

90% distillation temperature (T90) means the temperature at which 90% ofthe fuel evaporates expressed to the nearest degree Fahrenheit inaccordance with 13 CCR, section 2263.

Toxic air contaminants means exhaust emissions of benzene,1,3-butadiene, formaldehyde, and acetaldehyde.

The pollutants addressed by the foregoing specifications include oxidesof nitrogen (NO_(x)), and hydrocarbons (HC), which are generallymeasured in units of gm/mile, and potency-weighted toxics (PWT), whichare generally measured in units of mg/mile.

The Phase 2 reformulated gasoline regulations define a comprehensive setof specifications for gasoline (Table 1). These specifications have beendesigned to achieve large reductions in emissions of criteria and toxicair contaminants from gasoline-fueled vehicles. Gasolines which do notmeet the specifications are believed to be inferior with regard to theemissions which result from their use in vehicles. All gasolines sold inCalifornia, beginning Jun. 1, 1996, have had to meet CARB's Phase 2requirements as descried below. The specifications address the followingeight gasoline properties:

-   -   Reid vapor pressure (RVP)    -   Sulfur    -   Oxygen    -   Aromatic hydrocarbons    -   Benzene    -   Olefins    -   Temperature at which 90 percent of the fuel has evaporated (T90)    -   Temperature at which 50 percent of the fuel has evaporated (T50)

The Phase 2 gasoline regulations include gasoline specifications thatmust be met at the time the gasoline is supplied from the productionfacility. Producers have the option of meeting either “flat” limits or,if available, “averaging” limits, or, alternatively a Predictive Modelequivalent performance standard.

The flat limits must not be exceeded in any gallon of gasoline leavingthe production facility. For example, the aromatic content of gasoline,subject to the flat limit, could not exceed 25 volume percent (see Table1).

The averaging limits for each fuel property established in theregulations are numerically more stringent than the comparable flatlimits for that property. Under the averaging option, the producer mayassign differing “designated alternative limits” (DALs) to differentbatches of gasoline being supplied from the production facility. Eachbatch of gasoline must meed the DAL assigned for the batch. In addition,a producer supplying a batch of gasoline with a DAL less stringent thanthe averaging limit must, within 90 days before or after, supply fromthe same facility sufficient quantities of gasoline subject to morestringent DALs to fully offset the exceedances of the averaging limit.

The Phase 2 gasoline regulations also contain “cap” limits. The caplimits are absolute limits that cannot be exceeded in any gallon ofgasoline sold or supplied throughout the gasoline distribution system.These cap limits are of particular importance when the CaliforniaPredictive Model or averaging is used.

A mathematical model, the California Predictive Model, has also beendeveloped by CARB to allow refiners more flexibility. Use of thepredictive model is designed to allow producers to comply with the Phase2 gasoline requirements by producing gasoline to specifications slightlydifferent from either the averaging or flat limit specifications setforth in the regulations. However, producers must demonstrate that thealternative Phase 2 gasoline specifications will result in equivalent orlower emissions compared to Phase 2 gasoline meeting either the flat oraveraging limits as indicated by the Predictive Model. Further, the caplimits must be met for all gasoline formulations, even alternativeformulations allowed under the California Predictive Model. When thePredictive Model is used, the eight parameters of Table 1 are limited tothe cap limits.

In general, the California Predictive Model is a set of mathematicalequations that allows one to compare the expected exhaust emissionsperformance of a gasoline with a particular set of fuel properties tothe expected exhaust emissions performance of an appropriate gasolinefuel. One or more selected fuel properties can be changed when makingthis comparison.

Generally, in a predictive model, separate mathematical equations applyto different indicators. For example, a mathematical equation could bedeveloped for an air pollutant such as hydrocarbons; or, a mathematicalequation could be developed for a different air pollutant such as theoxides of nitrogen.

Generally, a predictive model for vehicle emissions is typicallycharacterized by:

-   -   the number of mathematical equations developed,    -   the number and type of motor vehicle emissions tests used in the        development of the mathematical equations, and    -   the mathematical or statistical approach used to analyze the        results of the emissions tests.

The California Predictive Model is comprised of twelve mathematicalequations. One set of six equations predicts emissions from vehicles inTechnology Class 3 (model years 1981-1985), another set of six is forTechnology Class 4 (model years 1986-1993). For each technology class,one equation estimates the relative amount of exhaust emissions ofhydrocarbons, the second estimates the relative amount of exhaustemissions of oxides of nitrogen, and four are used to estimate therelative amounts of exhaust emissions of the four toxic aircontaminants: benzene, 1,3-butadiene, acetaldehyde, and formaldehyde.These toxic air contaminants are combined based on their relativepotential to cause cancer, which is referred to as potency-weighting.

In creating the California Predictive Model, CARB compiled and analyzedthe results of over 7,300 vehicle exhaust emissions tests. A standardstatistical approach to develop the mathematical equations to estimatechanges in exhaust emissions was used based upon the data collected.

In summary, specific requirements were created by the California AirResources Board to restrict the formulation of gasoline to ensure theproduction of gasoline which produces low emissions when used inautomobiles.

The gasoline formulations of the present invention, however, containsubstantially no oxygenates. By substantially no oxygenates, it is meantthat the gasoline formulation contains less than at least one weightpercent oxygen, or preferably less than 0.5 weight percent oxygen, andmost preferably substantially zero weight percent oxygen. Thus, for thepurposes of the present invention, if some oxygen containing compoundsare contained in the gasoline formulation, the amount must be far lessthan that specified for California Phase 2 gasoline when oxygenates arerequired. Basically, the gasoline formulations of the present inventioncontain substantially no oxygenates.

Despite the removal of oxygenates, the gasoline formulations of thepresent invention also offer the advantage of good emissions. This isthe case even though the gasoline formulations also fail to meet theequivalent performance standard of the California Predictive Model. Ithas been surprisingly found that despite not meeting the PredictiveModel requirements for reformulated gasolines, the gasolines of thepresent invention offer good performance, and surprisingly low NO_(x)emissions. In fact, the gasolines of the present invention offer NO_(x)emissions performance which is substantially better than that predictedby the California Predictive Model.

The unleaded gasoline fuel of the present invention first requires thatit be substantially free of oxygenates. The fuel also exhibits a Reidvapor pressure of less than 7.5 psi, more preferably 7.0 or less, and asulfur content of less than 30 ppmw, more preferably less than 20 ppmw,even more preferably less than 15 ppmw, and most preferably about 10ppmw or less. It is also preferred that the gasoline fuel have an olefincontent no greater than 8 volume percent, preferably 6 volume percent orless, more preferably 5 volume percent or less, and most preferablyabout 2-3 volume percent or less. The unleaded gasoline fuel also has anaromatic hydrocarbon content between 25 and 30 volume percent, and/or a50% D-86 Distillation Temperature between 210 and 220° F., and/or a 90%distillation temperature of between 300 and 330° F.

Among other factors, therefore, the present invention is based upon thediscovery that one can substantially remove all oxygen containingcompounds from a fuel formulation, be within the cap limits prescribedby CARB, but fail to meed the flat limits for at least one, if not more,of the aromatics, T50 and T90 requirements for new (Phase 2)reformulated gasoline, fail the California Predictive Model, and stillobtain an excellent gasoline which exhibits low emissions. By observingthe Reid vapor pressure and low sulfur, and preferably low olefincontent requirements of the present invention, a gasoline fuel can beobtained which offers a substantially oxygenate free formulationallowing more flexibility to the refiner, but without sacrificing lowemissions. The gasoline formulations of the present invention areparticularly advantageous with regard to nitrogen oxide emissions(NO_(x)), for which there is increased concern with regard to theenvironment.

The gasoline fuel compositions of the present invention are applicableto all gasoline fueled cars, particularly those equipped with acatalytic converter, but have been found to be most advantageous fornewer gasoline fueled automobiles, and in particular vehicles certifiedto California Low Emission Vehicle (LEV) standards and beyond. For it isin such newer model cars, as exemplified by the 1998 Ford Contour with a2.0 liter engine, and 1997 Nissan Altima with a 2.4 liter engine, bothcertified to Transitional Low Emissions Vehicles (TLEV) standards, thatparticular advantages are seen with regard to NO_(x) emissions, whilealso observing acceptable emissions with regard to exhaust hydrocarbons.The gasoline fuel compositions of the present invention are also usefulthroughout the year, with perhaps some modification in the RVP forseasonal requirements.

In a preferred embodiment of the present invention, the unleadedgasoline fuel is substantially free of oxygenates, has a Reid vaporpressure of less than 7.5 psi and has a sulfur content of less than 30ppmw. The aromatic hydrocarbon content is greater than 25 volume percentbut less than 30, the 50% D-86 Distillation Point is no greater than220° F., and preferably no greater than 210° F., and the 90% D-86Distillation Point is no greater than 330° F., and preferably no greaterthan 300° F. The unleaded gasoline fuel also preferably has an olefincontent of 8 volume percent or less, more preferably 5 volume percent orless, and most preferably about 2-3 volume percent or less. The gasolinefuel also fails to meet the requirements of the present CaliforniaPredictive Model for emissions.

In another preferred embodiment of the present invention, the unleadedgasoline fuel of the present invention is substantially free ofoxygenates, has a Reid vapor pressure less than 7.5 psi, and has asulfur content of less than 30 ppmw. The aromatic hydrocarbon content isno greater than 30 volume percent, and preferably no greater than 25volume percent, and the fuel has a 50% D-86 Distillation Point greaterthan 210° F. but less than 220° F. The fuel also has a 90% D-86Distillation Point no greater than 330° F., and preferably no greaterthan 300° F. Preferably, the olefin content of the gasoline fuel is 8volume percent or less, more preferably 5 volume percent or less, andmost preferably about 2-3 volume percent or less. The gasoline fuel alsofails the present California Predictive Model requirements foremissions.

In another preferred embodiment of the present invention, the unleadedgasoline fuel is substantially free of oxygenates, has a Reid vaporpressure of less than 7.5 psi, and has a sulfur content of less than 30ppmw. The aromatic hydrocarbon content is no greater than 30 volumepercent, and preferably no greater than 25 volume percent, and the fuelhas a 50% D-86 Distillation Point no greater than 220° F., andpreferably no greater than 210° F. The fuel also has 90% D-86Distillation Point greater than 300° F., but no greater than 330° F. Itis most preferred that the olefin content of the gasoline fuel is also 8volume percent or less, more preferably 5 volume percent or less, andmost preferably about 2-3 volume percent or less. The gasoline fuel alsofails the present California Predictive Model requirements foremissions.

In the preferred embodiments of the present invention, in general, theReid vapor pressure of the gasoline fuels of the present invention areless than 7.5 psi, but are most preferably no greater than 7.0. Thesulfur content of the gasoline fuels of the present invention is lessthan 30 ppmw, and more preferably less than 20 ppmw. In the mostpreferred embodiments, the amount of sulfur contained in the unleadedgasoline fuels of the present invention is less than 15 ppmw sulfur,with the most preferred embodiment involving an unleaded gasoline fuelwhich contains no greater than 10 ppmw sulfur. It is further preferredthat the olefin content be low, for the low olefin content is believedto enhance the low sulfur effects and provide excellent performance.Therefore, the olefin content is preferably 8 volume percent or less,more preferably 6 volume percent or less, even more preferably 5 volumepercent or less, and most preferably about 3 volume percent, even 2volume percent, or less.

Generally, the lower the sulfur content, the more magnified thebeneficial effects. Thus, in order to obtain more flexibility,particularly with regard to the aromatics, T-50 and T-90characteristics, a lower sulfur content would be preferred. As mentionedpreviously, lower olefin content appears to enhance the beneficialeffects of the low sulfur. Therefore, lowering the olefin content incombination with the low sulfur can also help add flexibility to theblending of a gasoline formulation which exhibits good emissions.

The fuels of the present invention are useful in operating automotivevehicles having a spark-ignited internal combustion engine. These fuelsperform particularly well in vehicles designed for low exhaustemissions. These include vehicles certified to California Low EmissionsVehicle (LEV) standards and soon to be established Phase 2 LEV standards(LEV II) as well as U.S. Environmental Protection Agency National LowEmissions Vehicle (NLEV) standards, and soon to be established Tier 2standards. The fuels are introduced into the engine and then combustedin the engine. In a preferred embodiment, the automotive vehicle alsohas a catalytic converter into which at least some of the engine exhaustemissions created by combusting the unleaded gasoline are introduced.The resulting emissions are then discharged from the vehicle exhaustsystem to the atmosphere. Most of the emissions are inert, non-harmfulcomponents, with the regulated components such as hydrocarbons andNO_(x) being low. In particular, the emissions have a reduced amount ofNO_(x) emissions. The NO_(x) emissions can surprisingly surpass even thelevel indicated by the Predictive Model developed by the California AirResources Board with reference to a baseline fuel. In all cases, thepotency-weighted toxic requirements should also be met by means of thereduced amount of oxygenates and olefins and appropriate limits on theamount of benzene

The invention will be illustrated in greater detail by the followingExample. It is understood that the Example is given by way ofillustration and is not meant to limit the disclosure or the claims tofollow.

EXAMPLE

If the following test procedures were followed, it is believed that thecompositions listed in Table 2 would exemplify fuels in accordance withthe present invention which would exhibit surprising emissionsreductions.

All test fuels are stored in barrels in a refrigerated space maintainedat 50±5° F. Barrels remain in the storage area for a minimum of 24 hoursprior to being opened. They remain in a cooled area until they aredepleted or the test program is completed. RVP (Reid vapor pressure)samples are drawn from the barrels when they are opened (100%) and asthey approach depletion (10-20% capacity). RVP determinations are madewith a Grabner Instruments CCA-VPS vapor pressure tester. Each batch ofsamples include a cyclopentane reference sample to insure analyzerintegrity.

Testing is performed in accordance with “California Exhaust . . .Standards and Test Procedures for 1988 and Subsequent Model . . .Vehicles” (CCR Sec. 1960. 1), except those portions relating toevaporative emissions. Additional preconditioning is performed to insurethat as much of the fuel from previous tests as possible is drained andremoved from the fuel tank and fuel delivery system. Thispreconditioning ends with a standard drain and fill to 40% capacity,UDDS dynamometer preconditioning, and overnight soak prior to theexhaust emissions test.

Each vehicle receives a minimum of one test with each of the test fuels.The order of testing is completely randomized for each vehicle. Alltests on a given vehicle are performed consecutively—vehicles are notleft idle for extended periods while other program vehicles are beingtested. The tests on a vehicle are performed on consecutive days.

Fuel injected vehicles generally provide an access port in thepressurized fuel line which is used to drain the vehicle fuel tank byactivating the on-board fuel pump. A significant amount of fuel remainsin the fuel tank below the fuel pump pickup, however. Repeated fills anddrains are performed to dilute the fuel from a previous test with fuelfor the upcoming test. Some engine operation is also required to purgethe fuel line from the tank to the engine and from any bypass from thefuel rail back to the fuel tank. Modern feedback engine control systemsalso feature adaptive learning subsystems to provide baselineinformation regarding previous engine operation while the engine iswarming up. Preconditioning is designed to insure that any calibrationchanges resulting from the adaptive learning process are fully completedwith the new fuel.

The preconditioning procedure includes:

-   -   1. Draining tank and adding 20-25% fill of fresh test fuel.        Idling engine for 5 minutes.    -   2. Draining tank and adding 20-25% fill of fresh test fuel.        Performing one LA-4 and one HFET schedule on the dynamometer.    -   3. Soaking vehicle in controlled temperature soak room for a        minimum of one hour.    -   4. Draining and filling to 40% capacity with fresh test fuel.        Performing LA-4 dynamometer preconditioning. Soaking in        controlled temperature soak room until the vehicle was        transferred to the test cell for the FTP.

The multiple drains and fills insure that the amount of fuel remainingfrom previous tests is minimized. The engine operation and soaks provideample opportunity for any adaptive learning process to stabilize withthe new fuel. The final steps insure compliance with the CCRrequirements for the exhaust emission test.

The FTP exhaust emissions test includes measurement of non-methanehydrocarbons (NMHC), and NO_(x) in accordance with Federal andCalifornia test procedures.

GC bag samples are collected for each test phase of the FTP (3 bags),with dilution air sample collection of the Cold Transient and Stablephase combined, and the Hot Transient Phase (2 background bags). GCsamples are collected on tests of the vehicle.

Subtle changes in exhaust emissions and fuel economy may be overshadowedby test to test variability. Changes in some fuel properties typicallyresult in small, difficult to measure, changes in exhaust emissions.Procedures developed for ASTM testing of fuel efficient engine oils havebeen demonstrated to greatly improve test repeatability such thatcareful attention is given to preconditioning and soak conditions tofurther assure consistency in the tests. The compositions listed inTable 2 exemplify compositions in accordance with the invention, whichif tested as described above, would demonstrate low emissions.

TABLE 2 Test Fuels Fuel Fuel Fuel Fuel Fuel Fuel Fuel Fuel Fuel FuelFuel Fuel A B C D E Fuel F Fuel G H I J K Fuel L M N O Oxygen (wt %) 0 00 0 0.5 0.75 0.25 0 0 0 0 0.25 0 0 0 Aromatics (vol %) 30 28 28 27 25 2225 28 22 25 28 22 25 28 25 Olefins (vol %) 2 8 8 4 4 5 3 2 2 6 2 6 2 2 3Temperature at 50% 220 215 210 215 210 215 210 210 215 220 210 210 220210 215 distilled (° F.) Temperature at 90% 300 310 320 320 305 300 320320 300 290 300 320 290 310 315 distilled (° F.) Sulfur (ppmw) 30 20 1015 15 15 10 10 15 20 15 10 10 5 10 Benzene (vol %) 0.6 0.6 0.5 0.7 1.01.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Reid Vapor (psi) Pressure 7.5 77 7 7.5 7.0 7.0 7.0 7.5 7.0 7.0 7.0 7.0 7.0 7.0

One of the main advantages of the invention is that a less pollutingsubstantially oxygenate free gasoline fuel is provided that can be moreeasily prepared in a petroleum refinery or the like. That is, in atypical refinery in which gasoline is produced for sale, particularly inCalifornia, it is necessary or at least desirable in most instances toblend the hydrocarbon stocks so as to produce gasolines of specifiedReid vapor pressure, aromatic content, etc., and which meet all of theCARB Phase 2 gasoline requirements. In addition, the gasoline must meetother specifications, such as octane to assure good performance of theautomobile. Thus, the only difference is that now the refinery willblend the stocks in light of the information provided herein such thatthe emissions are reduced, particularly the NO_(x) emissions, as much asrequired or practicable, given the individual situation (the blendstocks available, refinery capacity, etc.) facing the particularrefinery. By following the present invention, additional flexibility isoffered in blending the fuels, particularly with regard to the aromatichydrocarbon content, the T50 and T90 specifications. Yet, anenvironmentally friendly fuel is provided which offers good performanceand surprisingly low NO_(x) emissions, as well as flexibility inblending.

While the invention has been described with preferred embodiments, it isto be understood that variations and modifications may be resorted to aswill be apparent to those skilled in the art. Such variations andmodifications are to be considered within the purview and the scope ofthe claims appended hereto.

1. An unleaded gasoline fuel, which is substantially free of oxygenatesand has a Reid vapor pressure less than 7.5 psi; a sulfur content lessthan 10 ppmw; an aromatics content of greater 25 volume percent but nogreater than 30 volume percent; and the fuel composition fails theCalifornia Predictive Model requirements for emissions.
 2. The unleadedgasoline fuel of claim 1, wherein the olefin content is 8.0 volumepercent or less.
 3. The unleaded gasoline fuel of claim 2, wherein thefuel has a Reid vapor pressure no greater than 7.0.
 4. The unleadedgasoline fuel of claim 2, wherein the olefin content of the fuel is 6volume percent or less.
 5. The unleaded gasoline fuel of claim 2,wherein the olefin content of the fuel is 5 volume percent or less. 6.The unleaded gasoline fuel of claim 2, wherein the olefin content of thefuel is 3 volume percent or less.
 7. The unleaded gasoline fuel of claim2, wherein the olefin content of the fuel is no greater than about 2volume percent.
 8. The unleaded gasoline fuel of claim 2, wherein thefuel has a 50% D-86 Distillation Point no greater than 210° F.
 9. Theunleaded gasoline fuel of claim 2, wherein the fuel has a 90% D-86Distillation Temperature no greater than 300° F.
 10. The unleadedgasoline fuel of claim 1, wherein the fuel has a 50% D-86 DistillationTemperature between 210 and 220° F., and/or a 90% D-86 DistillationTemperature between 300 and 330° F.
 11. An unleaded gasoline fuel, whichis substantially free of oxygenates and has a Reid vapor pressure lessthan 7.5 psi; a sulfur content less than 10 ppmw; and a 50% D-86Distillation Temperature greater than 210 but no greater than 220° F.,and the fuel composition fails the California Predictive Modelrequirements for emissions.
 12. The unleaded gasoline fuel of claim 11,wherein the olefin content is 8 volume percent or less.
 13. The unleadedgasoline fuel of claim 12, wherein the fuel has a Reid vapor pressure nogreater than 7.0.
 14. The unleaded gasoline fuel of claim 12, whereinthe olefin fuel content is 6 volume percent or less.
 15. The unleadedgasoline fuel of claim 12, wherein the olefin fuel content is 5 volumepercent or less.
 16. The unleaded gasoline fuel of claim 12, wherein theolefin fuel content is 3 volume percent or less.
 17. The unleadedgasoline fuel of claim 12, wherein the olefin fuel content is no greaterthan about 2 volume percent.
 18. The unleaded gasoline fuel of claim 12,wherein the aromatic hydrocarbon content is no greater than 25 volumepercent.
 19. The unleaded gasoline fuel of claim 12, wherein the fuelhas a 90% D-86 Distillation Temperature no greater than 300° F.
 20. Theunleaded gasoline fuel of claim 12, wherein the fuel has an aromatichydrocarbon content between 25 and 30 volume percent, and/or a 90% D-86Distillation Temperature between 300 and 330° F.
 21. An unleadedgasoline fuel, which is substantially free of oxygenates and has a Reidvapor pressure less than 7.5 psi; a sulfur content less than 10 ppmw;and a 90% D-86 Distillation Temperature between 300 and 330° F., and thefuel composition fails the California Predictive Model requirements foremissions.
 22. The unleaded gasoline fuel of claim 21, wherein theolefin content is 8 volume percent or less.
 23. The unleaded gasolinefuel of claim 22, wherein the fuel has a Reid vapor pressure no greaterthan 7.0.
 24. The unleaded gasoline fuel of claim 22, wherein the olefinfuel content is 5 volume percent or less.
 25. The unleaded gasoline fuelof claim 22, wherein the olefin fuel content is 3 volume percent orless.
 26. The unleaded gasoline fuel of claim 22, wherein the olefinfuel content is no greater than about 2 volume percent.
 27. The unleadedgasoline fuel of claim 22, wherein the aromatic hydrocarbon content isno greater than 25 volume percent.
 28. The unleaded gasoline fuel ofclaim 22, wherein the fuel has a 50% D-86 Distillation Point no greaterthan 210° F.
 29. The unleaded gasoline fuel of claim 22, wherein thefuel has an aromatic hydrocarbon content between 25 and 30 volumepercent, and/or a 50% D-86 Distillation Temperature between 210 and 220°F.
 30. A method for operating an automotive vehicle having aspark-ignited, internal combustion engine, comprising: introducing intothe engine the unleaded gasoline fuel of claim 1, and then combustingthe unleaded gasoline in the engine.
 31. The method of claim 30, whereinthe automotive vehicle also has a catalytic converter into which atleast some of the engine exhaust emissions created by combusting theunleaded gasoline is introduced, with emissions then being dischargedfrom the catalytic converter and subsequently to the atmosphere.
 32. Themethod of claim 30, wherein the introduction into the engine of anunleaded gasoline is accomplished by fuel injection.
 33. The method ofclaim 31, wherein the introduction into the engine of an unleadedgasoline is accomplished by fuel injection.
 34. The method of claim 31,wherein the gasoline introduced into the engine has a Reid vaporpressure no greater than 7.0.
 35. The method of claim 31, wherein thegasoline introduced into the engine contains 5 volume percent olefin orless.
 36. The method of claim 35, wherein the gasoline fuel introducedinto the engine has an olefin content of 3 volume percent or less. 37.The method of claim 35, wherein the gasoline has an olefin content of nogreater than 2 volume percent.
 38. A method for operating an automotivevehicle having a spark-ignited, internal combustion engine, comprising:introducing into the engine the unleaded gasoline fuel of claim 15, andthen combusting the unleaded gasoline in the engine.
 39. The method ofclaim 38, wherein the automotive vehicle also has a catalytic converterinto which at least some of the engine exhaust emissions created bycombusting the unleaded gasoline is introduced, with emissions thenbeing discharged from the catalytic converter and subsequently to theatmosphere.
 40. The method of claim 38, wherein the introduction intothe engine of an unleaded gasoline is accomplished by fuel injection.41. The method of claim 39, wherein the introduction into the engine ofan unleaded gasoline is accomplished by fuel injection.
 42. The methodof claim 39, wherein the gasoline introduced into the engine has a Reidvapor pressure no greater than 7.0.
 43. The method of claim 39, whereinthe gasoline introduced into the engine contains 5 volume percent olefinor less.
 44. The method of claim 39, wherein the gasoline fuelintroduced into the engine has an olefin content of 3 volume percent orless.
 45. The method of claim 39, wherein the gasoline has an olefincontent of no greater than 2 volume percent.
 46. A method for operatingan automotive vehicle having a spark-ignited, internal combustionengine, comprising: introducing into the engine the unleaded gasolinefuel of claim 21, and then combusting the unleaded gasoline in theengine.
 47. The method of claim 46, wherein the automotive vehicle alsohas a catalytic converter into which at least some of the engine exhaustemissions created by combusting the unleaded gasoline is introduced,with emissions then being discharged from the catalytic converter andsubsequently to the atmosphere.
 48. The method of claim 46, wherein theintroduction into the engine of an unleaded gasoline is accomplished byfuel injection.
 49. The method of claim 47, wherein the introductioninto the engine of an unleaded gasoline is accomplished by fuelinjection.
 50. The method of claim 47, wherein the gasoline introducedinto the engine has a Reid vapor pressure no greater than 7.0.
 51. Themethod of claim 47, wherein the gasoline introduced into the enginecontains 5 volume percent olefin or less.
 52. The method of claim 47,wherein the gasoline fuel introduced into the engine has an olefincontent of 3 volume percent or less.
 53. The method of claim 47, whereinthe gasoline has an olefin content of no greater than 2 volume percent.